Because we didn't care about Poland in 1939 and look where that got us.
Out of curiosity, how many wars did China engage in since 1979? Also, there are no racial ideology in China simiar to Germany in the 1930s. The Uyghur deradicalization centres are made because of frequent terorist attacks from this particular group. Hui Muslims are not subject to deradicalization.
In regards to South China Sea disputes. It is not a China problem. All other ASEAN countries are also disputing with each other about what portion of the Sea belongs to them. This is not even counting other border disputes in Asian seas (e.g. Malaysia vs. Indonesia).
Let's have a candid two-way discussion. Give me some intuition into your assesment that China is 1930s Germany.